Sheet or paper feed mechanisms for feeding the first sheet from a stack of sheets commonly employ feed wheels. These wheels move into engagement with the exposed sheet, to cause the separating and feeding of the sheet, usually by an initial buckling movement of the sheet, followed by the release of the sheet from the stack so that the sheet may be fed through take-away rolls from the stack. Both forward and reverse buckling concepts have been employed. In either case, the feed wheels usually remain at a fixed location in relation to the stack, during sheet feeding.
A particular problem arises in the feeding of paper from a stack, in which the paper has a soft coating or is otherwise sensitive to pressure. An example of sheets having a soft coating, which may be easily damaged by excessive localized pressure, are the receiver sheets disclosed and described in U.S. Pat. No. 4,399,209 assigned to the same assignee as this invention. The feeding of such sheets is complicated by the tendency for the mechanical locking between the adjacent sheets, due to the relatively high co-efficient of friction of the sheet surfaces.
In such systems, the feed wheels create a pressure on the second sheet (n+1) at a location directly under the feed wheels, which pressure can cause damage such as skid marks on the second sheet, since this sheet remains stationary in relation to the feed wheels while the first sheet is moved. The first sheet damages the second sheet by skidding over one location while under pressure from the feed wheels.
Previous attempts to reduce the problem have involved the positioning of the take-away rolls so that the dispensed sheet is removed immediately after feeding by the fixed feed wheels. However, with a distance as short as one inch, damage has been observed on the second or underlying sheet.
Additional attempts to control pressure and to provide a non-marking feed construction have involved the use of relatively thick foam rubber pads on a top sheet contacting member. By relatively thick, it is meant that the aspect ratio of the pads, thickness to length in the process direction, was from about 1 to 1 to 3 to 1. Such thick pad contacting devices proved to be unsatisfactory for the feeding of soft coated and pressure sensitive media material of the type defined above, primarily in view of the tendency of the material to roll or tilt, or pitch. In such devices, the tendency is for the leading or forward edge to pitch against the sheet being processed with concomitant lifting of the rear or trailing edge, due to the lack of rigidity of such blocks in the process direction.